1. Field of the Invention
The present invention relates to a technique for detecting alteration of digital data.
2. Description of the Related Art
Recently, with the rapid development and proliferation of computers and networks, various information such as text data, image data, and audio data have been digitalized. Digital data does not deteriorate with time, and therefore can remain in its original state. In addition, digital data can be easily copied, edited, and processed. Although the easy copying, editing, and processing of digital data are very useful for users, digital data security has become a major concern. Accordingly, security techniques for digital data have been rapidly becoming increasingly important.
As a technique that allows a recipient to detect whether received data has been altered, a digital signature technique has been proposed. The digital signature is additional data that is used for preventing original data from being altered. In addition, the digital signature technique can effectively prevent not only data alteration but also spoofing and repudiation on the Internet.
As disclosed in U.S. Pat. No. 5,898,779, a signature method intended for the verification of data included in a partial area of an image is proposed. The digital image signature method disclosed in U.S. Pat. No. 5,898,779 is performed as follows: first, selecting the ROI of an image; calculating the hash value of the selected ROI; generating a digital signature by encrypting the calculated hash value using a private key; and then attaching the digital signature to the image.
Currently, various electronic documents including digital data are used. When an electronic document is reused, the entire electronic document is typically not reused, instead a component of the electronic document is often reused. For example, the case can be considered where text data such as a predetermined word, sentence, line, or paragraph, predetermined image data, or predetermined graphic data is reused in such a manner that it is copied and is then attached to another document.
Although U.S. Pat. No. 5,898,779 describes the technique enabling verification of whether data of an area included in original image data has been altered, it does not disclose at all about reuse of a certain component included in the original image data. Therefore, it does not disclose a technique of affixing a signature to data that is reusing a certain component included in the original image data.